1. Field of the Invention
The present invention relates to an energy retrievable data driver, an energy retrievable display, and an energy retrievable method of driving a display.
2. Discussion of Related Art
A display divides a black-and-white or color image into pixels, loads screen information into each pixel and thereby display the image. A color display system generally displays each pixel of an image in the three primary colors of red, green and blue (RGB). An actual display requires a light source and it is possible to depend on a backlight as in a liquid crystal display (LCD) or use devices whose pixels self-emit light such as an organic light emitting diodes (OLED).
Power consumption in a display system may be roughly classified into the following three types: power consumed by a timing controller which converts a display source input for driving pixels into data required for driving a screen, power consumed by a driver integrated circuit (IC) which drives the pixels, and power consumed by a display to emit light. Among these, the last power consumption is the largest and determined by the light source used. In the case of an OLED display, the last power consumption is dependent on screen brightness data and so on.
The second largest power is consumed by the driver IC. A display system with a quarter high-definition (QHD) resolution has 2560×1440 pixels, and the actual number of channels is 2560*3=7680 because each pixel has the three colors of RGB. In practice, it is impossible to manufacture a single driver IC having such a large number of channels, and thus a system is configured with a plurality of easily manufactured driver ICs having a number of channels such as 720 channels or 960 channels. When a display system uses driver ICs having 960 channels, a total of eight ICs are required. A large-scale display in accordance with a recent trend has a resistance and a line capacitance of tens of pico-farads or more on a path from a data driver IC to an actual pixel. When a display system is driven at 60 Hz, it is possible to see that a line drive time is 1/(60*1440)=11.5 μs and a driving frequency is about 87 kHz. In other words, a display system with a QHD resolution may be simplified as 7680 driver circuits which charge and discharge 7680 capacitors of tens of pico-farads with a frequency of 87 kHz.
An active matrix LCD (AMLCD) is supplied with an alternating current (AC) signal based on a common electrode connected to a liquid crystal. In the frame inversion or line inversion method, a power source of a common electrode signal is changed between plus and minus with respect to the signal to exhibit the same characteristic as an AC signal. However, in practice, the capacitance of a common electrode is too high to be efficient in terms of power consumption. In the dot inversion method which is another driving method, an output of a column driver is driven higher or lower than a fixed common electrode signal to exhibit the same characteristic as an AC signal.
An active matrix OLED (AMOLED) display has no common electrode, and does not require an AC signal. Therefore, the power consumption of a column driver is larger than the power consumption of a column driver in an AMLCD, and it is difficult to reduce the power consumption with the existing data driver.
A power consumed by a capacitance may be calculated as C*{V22−V12}*f*N. When a capacitance is 50 pF, a total number of lines is 7680, a driving frequency is 87 kHz, V2 is 7 V, and V1 is 2 V, the calculated power consumption is about 1.5 [W]. These days, timing controllers are manufactured using a fine scale process, and thus have a power consumption of about 100 mW to 200 mW, so that, excluding the light source, a data driver consumes most of the power.
Since the above calculation is based on an assumption of the worst case, a power consumption is a probabilistic average in practice. However, due to the recent requirements of high picture quality and requirements for videos, the power consumption increases in portable devices such as a smart phone, a tablet personal computer (PC), and so on. In the case of the portable devices such as a smart phone and a tablet PC, the power consumed by a display is a considerable portion of the power consumed by. To increase a usage time, there is a need to minimize the power consumption of the display.